The Hedgehog (Hh) family of secreted proteins mediates a variety of short- range cell signalling events in development of Drosophila and several vertebrates. The long term objectives of this research are to understand Hh signal transduction and its integration with other cellular processes. Hb has been proposed to act as a morphogen, with specific levels of Hh signal specifying unique responses. The principal goal of the work is to determine how different levels of Hh signaling lead to qualitatively different responses. Recent genetic and molecular evidence supports the involvement of Smoothened (Smo), a putative seven transmembrane (7-TM) receptor, as a Hh receptor. The proposed research uses in vivo, cell culture, and biochemical approaches to explore the role of Smo in Hh signaling. Four Specific Aims outline the proposal: 1) Test for physical interaction between Hh and Smo, 2) Test for participation of heterotrimeric G proteins in Hh signaling, 3) Test for regulation of Smo by Patched, another cell surface protein, and 4) Test for regulation of Smo by Protein Kinase A. These experiments will explore the role and regulation of Smo in Hh signal transduction. The resulting description of Smo regulation could have profound implications in the broader context of 7-TM receptor-mediated physiology and biology. Hh signaling controls the generation of key neural populations which are depleted in diseases such as polio and Parkinson's. Understanding Hh signaling could lead to strategies for preventing the loss of or for replacing these neural populations.